Data recording medium, data recording method, and device

ABSTRACT

With data of four symbols (FIG.  11 A), a parity of two symbols (FIG.  11 B) is created. These six symbols are EFM-modulated. Each symbol of eight bits is converted into a pattern of 14 bits (FIG.  11 C). In a pit/land sequence formed on a disc (FIG.  11 D), two symbols are rewritten. One symbol is (0×40). When an additional recording process is performed for the bit/land sequence, the pit length becomes long (FIG.  11 E). The reproduced 14-bit data is converted into eight bits on the reproducing side. Thus, the original data (0×40) is rewritten to (0×22). A parity is also changed so that the additionally recorded data symbol (0×22) is not detected as an error.

TECHNICAL FIELD

[0001] The present invention relates to a data recording medium, a datarecording method, and a data recording apparatus that are applicable foran optical disc of for example a read-only disc (ROM).

BACKGROUND ART

[0002] The standard about compact discs (CD), which have been widelyused, is referred to as compact disc audio (CD-DA) and based on thedescription of a standard specification book called Redbook. Based onthe specification, various formats for example CD-ROM have beenstandardized and so-called CD family has been set forth. In thefollowing description, CD generally refers to discs of various formatsincluded in the CD family.

[0003] A technology of which a laser beam is irradiated on a properlyselected reflective film on a disc and thereby the lengths of pits arevaried has been proposed. This recording process is sometimes referredto as additional recording process. When data is additionally recordedon the reflective film, for example identification information thatidentifies each disc can be recorded. When identification information isrecorded in the CD format, a sub code of Q channel of the CD format canbe used.

[0004] In a CD, an error correction code referred to as CIRC (CrossInterleave Reed-Solomon Code) is used. Thus, when data such as discidentification information is recorded on a reflective film, data thatis additionally recorded is detected as an error and corrected with theCRIC. In this case, original data of which the additional recordingprocess has not been performed is read. If the error that exceeds theerror correction performance of the CIRC takes place, the error cannotbe corrected and data cannot be read. Alternatively, data that has beenadditionally recorded cannot be read because an interpolating process isperformed. Thus, so far, the proposed additional recording process hasbeen performed for only an area in which the error correction codeencoding process is not performed. Thus, the applicable range of theadditional recording process is restricted.

DISCLOSURE OF THE INVENTION

[0005] An object of the present invention is to provide a data recordingmedium, a data recording method, and a data recording apparatus thatallow an application range of the additional recording process to beextended.

[0006] To solve the foregoing problem, the present invention is a datarecording medium having a reflective film, a part of data in a recordingarea being rewritten by recording data encoded with an error correctioncode to the reflective film so that the data is not detected as an errorwhen the data is decoded.

[0007] The present invention is a data recording method for recordingdata on a data recording medium having a reflective film, a part of datain a recording area being rewritten by recording data encoded with anerror correction code to the reflective film so that the data is notdetected as an error when the data is decoded.

[0008] The present invention is a recording apparatus for recording dataon a data recording medium having a reflective film, a part of data in arecording area being rewritten by recording data encoded with an errorcorrection code to the reflective film so that the data is not detectedas an error when the data is decoded.

[0009] According to the present invention, data is additionally recordedon a reflective film so that when the date is decoded, the data is notdetected as an error. Thus, when data that has been encoded with anerror correction code is decoded, a problem of which rewritten datacannot be read does not take place. According to the present invention,since data can be additionally recorded in an area that has been encodedwith an error correction code, the applicable range of the additionalrecording process can be extended.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a schematic diagram describing a recording pattern and astructure of a conventional CD.

[0011]FIG. 2 is a schematic diagram describing a disc producing processaccording to an embodiment of the present invention.

[0012]FIG. 3 is a schematic diagram describing an additional recordingprocess according to the embodiment of the present invention.

[0013]FIG. 4 is a schematic diagram describing a recording format of anoptical disc according to the present invention.

[0014]FIG. 5 is a schematic diagram describing a recording format of theoptical disc according to the present invention.

[0015]FIG. 6 is a block diagram showing an example of a CIRC encoder.

[0016]FIG. 7 is a more detailed block diagram showing the example of theCIRC decoder.

[0017]FIG. 8 is a block diagram showing an example of a CIRC decoder.

[0018]FIG. 9 is a more detailed block diagram showing the example of theCIRC decoder.

[0019]FIG. 10 is a schematic diagram describing a CIRC interleavingprocess.

[0020]FIGS. 11A to H are schematic diagrams describing an additionalrecording process according to the embodiment of the present invention.

[0021]FIG. 12 is a schematic diagram describing an additional recordingprocess in the case the CIRC is used.

[0022]FIG. 13 is a schematic diagram describing the additional recordingprocess in the case that the CIRC is used.

[0023]FIG. 14 is a schematic diagram describing the additional recordingprocess in the case that the CIRC is used.

[0024]FIG. 15 is a schematic diagram describing the additional recordingprocess in the case that the CIRC is used.

BEST MODES FOR CARRYING OUT THE INVENTION

[0025] Next, an embodiment of which the present invention is applied tothe case that disc identification information (hereinafter referred toas UDI) is recorded on a disc shaped recording medium will be described.The UDI is information that identifies each disc. The UDI describes forexample disc production company name, disc seller name, productionfactory name, year of production, serial number, time information, andso forth. According to the present invention, the additionally recordedinformation is not limited to the UDI, but desired information. The UDIis recorded in such a manner that can be read by a conventional CDplayer or a conventional CD-ROM drive. First of all, for easyunderstanding, the structure of an optical disc for example a CD will bedescribed.

[0026]FIG. 1 is an enlarged view showing a part of a conventional CD.Concave portions that are referred to as pits and lands that are no-pitareas are alternately formed on tracks having a predetermined trackpitch (for example, 1.6 μm). The lengths of pits and lands are in therange from 3 T to 11 T where T represents the minimum inversioninterval. Laser light is irradiated from the rear surface of the CD.

[0027] The CD is composed of a transparent disc substrate 1 having athickness of 1.2 mm, a reflective film 2 coated thereon, and aprotection film 3 coated thereon. As the reflective film 2, one having ahigh reflectance is used. The CD is a read-only disc. However, as willbe described later, after the reflective film 2 is coated, information(UDI) is recorded on the reflective film 2 with the laser light.

[0028] Next, with reference to FIG. 2, a flow of the production processof the CD will be described. At step S1, a glass master on which photoresist, which is a photosensitive material, is coated on a glasssubstrate is rotated by a spindle motor. Laser light that is turnedon/off in accordance with a record signal is irradiated on the photoresist film. As a result, a master is produced. A developing process isperformed for the photo resist film is developed. When the resist is ofpositive type, the exposed portion is melted. An uneven pattern isformed on the photo resist film.

[0029] The photo resist master is plated by an electroplating method. Asa result, one metal master is produced (at step S2). With the metalmaster, a plurality of mothers are produced (at step S3). In addition,with the mother, a plurality of stampers are produced (at step S4). Withthe stamper, a disc substrate is produced. The disc substrate isproduced by the compression molding method, the injection moldingmethod, the light setting method, or the like. At step S6, a reflectivefilm and a protection film are coated. In the conventional discproduction method, a label is printed on the CD.

[0030] In the example, shown in FIG. 2, laser light is irradiated to thereflective film (a mirror portion, for example a land). In addition,information is additionally recorded at step S7. Laser light isirradiated on the reflective film. The land on the reflective film isheated (thermally recorded). As a result, atoms are traveled and thefilm structure and crystallization are varied. Thus, the reflectance ofthe portion decreases. As a result, after laser light is irradiated onthe land, the reflection of the laser light becomes small. Thus, a lightdetector recognizes the land as a pit. With this characteristics, thepit length can be varied so as to record information. In this case, thereflective film is made of a material that allows the reflectancethereof to be varied by laser irradiation. There is a material whosereflectance increases by the additional recording process.

[0031] In reality, the reflective film is made of an aluminum alloyAl_(100-y)X_(y) where X is at least one element selected from a groupconsisting of Ge, Ti, Ni, Si, Tb, Fe, and Ag. The composition rate y ofthe Al alloy film is selected in the range of 5<y<50 [atomic %].

[0032] Alternatively, the reflective film may be also made of an Agalloy film Ag_(100-z)Y_(z) where Y is at least one element selected froma group consisting of Ge, Ti, Ni, Si, Tb, Fe, and Al. The compositionrate z of the Al alloy film is selected in the range of 5<z<50 [atomic%]. The reflective film can be formed by for example the magnetronsputtering method.

[0033] For example, in the condition that the reflective film of AlGealloy is formed with a thickness of 50 nm, laser light is irradiatedfrom a transparent substrate side or a protection film side through anobjective lens, if the composition rate of Ge is 20 [atomic %] and therecording power is in the range from 6 to 7 [mW], the reflectancedecreases by around 6%. In such a condition, if the composition rate ofGe is 27.6 [atomic %] and the recording power is in the range from 5 to8 [mW], the reflectance decreases by 7 to 8%. Since the reflectancevaries in such a manner, the additional recording process can beperformed for the reflective film.

[0034]FIG. 3 is a schematic diagram practically describing a method foradditionally recording the UDI. There are two patterns depending on thepreceding pattern. The two patterns are referred to as pattern A andpattern B.

[0035] First, the pattern A will be described. Three merging bits forexample (000) are inserted between symbols. When the additionalrecording process is performed, a data symbol of eight bits is forexample (0×47) where 0× represents hexadecimal notation. FIG. 3 shows a14-bit pattern (00100100100100) of which the eight bits have beenmodulated in accordance with the EFM (eight to fourteen modulation)system.

[0036] A laser beam with which the additional recording process isperformed is irradiated in a hatched area between the two pits. As aresult, the reflectance of the hatched area decreases. After theadditional recording process has been performed, two pits are connectedand reproduced as one pit. In this case, the 14-bit pattern becomes(00100100000000). This is because when the 14-bit pattern isEFM-demodulated, it is demodulated as eight bits (0×07).

[0037] In the case of the pattern B, the merging bits are (001). In thiscase, as with the pattern A, when a laser beam is irradiated to thehatched area, eight bits can be varied from (0×47) to (0×07).

[0038] As described above, a data symbol (0×47) can be rewritten to(0×07). There are many types of data that can be additionally recorded.A data symbol (0×40) can be varied to (0×00). However, in the additionalrecording process, laser is irradiated to a mirror portion in which datahas been recorded so as to vary the pit length. Thus, the types of datathat can be additionally recorded are restricted.

[0039] Next, the error correction code encoding process used for a CDwill be described. In a CD, as an error correction code encoding system,the CIRC that dually performs an error correction code encoding processwith a C1 code sequence (in the vertical direction) and a C2 codesequence (in the diagonal direction). Data that has been encoded with anerror correction code is EFM-modulated in the unit of one frame.

[0040]FIG. 4 shows one frame of a data structure of a CD before the datahas been EFM modulated. When audio data is sampled with 16 bits, asshown in FIG. 4, one frame is composed of data bits of 24 symbols thatare equivalent to six sample words of each of L (left) and R (right)(one symbol is eight bits of which 16 bits are divided by two), a Qparity of four symbols, a P parity of four symbols, and a sub code ofone symbol. Data of one frame (also referred to as one EFM frame)recorded on the disc is converted from eight bits into 14 bits inaccordance with the EFM modulation. In addition, DC componentsuppression bits are added. Moreover, a frame sync is added.

[0041] Thus, one frame recorded on the disc is composed of: Frame sync24 channel bits Data bits 14 · 24 = 336 channel bits Sub code 14 channelbits Paritites 14 · 8 = 112 channel bits Merging bits 3 · 34 = 102channel bits

[0042] Thus, the total number of channel bits of one frame is 588channel bits.

[0043] In the EFM modulating system, each symbol (eight data bits) isconverted into 14 channel bits. The minimum time width Tmin of the EFMmodulation (the time width of which the number of 0s between 1s of arecording system) is 3 T. The pit length equivalent to 3 T is 0.87 μm.The pit length equivalent to T is the minimum pit length. In addition,three merging pits are placed between two blocks of 14 channel bits.Moreover, a frame sync pattern is added at the beginning of the frame.When the period of channel bits is T, a frame sync pattern is a patternof which 11 T, 11 T, and 2 T are successive. Such a pattern does nottake place in the EFM modulation rule. Thus, a frame sync can bedetected with a special pattern. One frame is composed of a total of 588channel bits. The frame frequency is 7.35 kHz.

[0044] A group of such 98 frames is referred to as sub code frame (orsub code block). The sub code frame is equivalent to {fraction (1/75)}second of a reproducing time of a conventional CD. FIG. 5 shows a subcode frame of which 98 frames are rearranged so that they are successivein the vertical direction. A sub code of one symbol of each frameincludes one bit of each of eight channels P to W. As shown in FIG. 5,one sector is composed of a period (98 frames) that completes a subcode. Sub codes of two beginning frames of 98 frames are sub code framesyncs S0 and S1. When data of an optical disc is recorded on such as aCD-ROM disc, 98 frames (2,352 bytes) that is a unit of which sub codesare completed are one sector.

[0045]FIG. 6 and FIG. 7 are block diagrams showing a flow of an encodingprocess in accordance with the CIRC system. 24 symbols of which one wordof an audio signal is divided into high order eight bits and low ordereight bits) (W12 n, A, W12 n, B, . . . , W12 n+12, A, W12 n+11, B) (thehigh order eight bits are denoted by A, whereas the low order eight bitsare denoted by B) are supplied to a two-symbol delay/scramble circuit11. Even word data L6 n, R6 n, L6 n+2, R6 n+2, . . . are delayed by twosymbols each. Even if all a sequence becomes error in a C2 encoder 12,it can interpolate the sequence. The two-symbol delay/scramble circuit11 can scramble data so that the maximum burst error interpolationlength can be obtained.

[0046] An output of the two-symbol delay/scramble circuit 11 is suppliedto the C2 encoder 12. The C2 encoder 12 performs an encoding processwith (28, 24, 5) Reed-Solomon code on GF (28) and generates a Q parityof four symbols Q12 n, Q12 n+1, Q12 n+2, and Q12 n+3. An output of 28symbols of the C2 encoder 12 is supplied to an interleave circuit 13.When a unit delay amount is denoted by D, the interleave circuit 13gives delay amounts that vary in arithmetic series such as 0, D, 2D, . .. , so that a first sequence of symbols is converted into a secondsequence. The interleave circuit 13 disperses a burst error.

[0047] An output of the interleave circuit 13 is supplied to a C1encoder 14. The C1 encoder 14 uses (32, 28, 5) Reed-Solomon code on GF(28) as a C1 code. The C1 encoder 14 generates a P parity of foursymbols P12 n, P12 n+1, P12 n+2, and P12+3. The minimum distance of eachof the C1 code and the C2 code is 5. Thus, a two-symbol error can becorrected. A four-symbol error can be erasure-corrected (in the casethat the position of an error symbol is known).

[0048] An output of 32 symbols of the C1 encoder 14 is supplied to aone-symbol delay circuit 15. The one-symbol delay circuit 15 makesadjacent symbols apart so as to prevent an error at the boundary ofsymbols from causing a two-symbol error. The Q parity is inverted by aninverter. Thus, even if data and parities become all zero, an error canbe detected.

[0049] The interleave circuit 13 has a unit delay amount D=4 frames.Adjacent symbols are apart by four frames. In the CIRC4 system, themaximum delay amount is 27D (=108 frames). The total interleave lengthis 109 frames.

[0050]FIG. 8 and FIG. 9 are block diagrams showing a flow of a decodingprocess. The decoding process is performed in the reverse order of theencoding process. Reproduced data that is output from the EFMdemodulating circuit is supplied to a one-symbol delay circuit 21. Thedelay of data by the one-symbol delay circuit 15 on the encoding side iscancelled by the circuit 21.

[0051] An output of 32 symbols of the one-symbol delay circuit 21 issupplied to a C1 decoder 22. An output of the C1 decoder 22 is suppliedto a de-interleave circuit 23. The de-interleave circuit 23 gives delayamounts that vary in arithmetic series such as 27D, 26D, . . . , D, and0 to 28 symbols so as to cancel the delays by the interleave circuit 13.The de-interleave circuit 23 has a unit delay amount D=4 frames.

[0052] As shown in FIG. 10, the unit delay amount D is (D=4). The totalinterleave length is 109 (=108+1) frames, which is slightly larger thanone sector. The total interleave length defines a correction performanceagainst a burst error of which many pieces of data successively becomeerrors due to a fingerprint adhered on a disc, a scratch thereon, and soforth. As the total interleave length is large, the correctionperformance of the burst error is high.

[0053] An output of the de-interleave circuit 23 is supplied to a C2decoder 24. The C2 decoder 24 performs a C2 code decoding process. Anoutput of 24 symbols of the C2 decoder 24 is supplied to a two-symboldelay/de-scramble circuit 25. From the two-symbol delay/de-scramblecircuit 25, decoded data of 24 symbols is obtained. An interpolationflag generating circuit 26 generates an interpolation flag with errorflags that are output from the C1 decoder 22 and the C2 decoder 24. Withthe interpolation flag, data that represents an error is interpolated.Thus, in the CIRC, the error correction code encoding process isperformed with the C1 code sequence in the vertical direction and withthe C2 code sequence in the diagonal direction. In other words, theerror correction code encoding process is dually performed.

[0054] According to the present invention, a part of data in an areathat has been encoded with an error correction code is rewritten so asto record desired data for example UDI. FIGS. 11A to H show an exampleof a data rewriting method. However, for easy understanding, FIGS. 11Ato H show an error correction code encoding process simpler than theCIRC. In other words, with data of four symbols (0×82, 0×ef, 0×75, and0×40) shown in FIG. 11A, a parity of two symbols (0×ba and 0×e2) shownin FIG. 11B is generated. This error correction code encoding processhas a performance for correcting a one-symbol error. Binary numbers ofreal parity symbols represent only code examples. For example, they areparity symbols of the Reed-Solomon code, not values that are obtained bycalculations of the error correction code encoding process.

[0055] These six symbols are EFM-modulated. As shown in FIG. 11C, eachsymbol of eight bits is converted into a pattern of 14 bits. Mergingbits are not added. In FIG. 11C, “1” represents an inversion of a level.A pit/land sequence as an uneven pattern on the disc is as shown in FIG.11D. The period of which “1s” are successive is the period of a pit,whereas the period of which “0s” are successive is the period of a land.

[0056] Next, as described with reference to FIG. 3, the additionalrecording process is performed. In FIG. 11, as represented with boxes,two symbols are rewritten. One symbol is originally (0×40). When theadditional recording process is performed for the pit/land sequenceshown in FIG. 11D, as shown in FIG. 11E, the pit length becomes long.When a pit/land sequence shown in FIG. 11E is reproduced after theadditional recording process has been performed, data of 14 bits shownin FIG. 11F is reproduced.

[0057] The data of 14 bits is converted into eight bits on thereproducing side. All read data shown in FIG. 11G is obtained. Thus,original data (0×40) is rewritten to (0×22). If only one symbol of sixsymbols of an error correction code sequence is changed, when they aredecoded, an error is detected and corrected. In other words, originaldata (0×40) is reproduced. In this case, the rewritten data (0×22)cannot be reproduced.

[0058] Thus, in the example shown in FIG. 11, a parity symbol (0×e2) ischanged to (0×01) so that a data symbol (0×22) that has beenadditionally recorded is not detected as an error when the data isdecoded. When six symbols (0×82, 0×ef, 0×75, 0×22, 0×ba, and 0×01) thatinclude a data symbol that has been rewritten and a parity symbol (0×01)are reproduced and decoded with an error correction code, no error isdetected. In other words, as parity symbols in the case that data (0×22)is included, (0×ba) and (0×01) have been obtained. Thus, as shown inFIG. 11H, a data symbol that has been rewritten can be reproduced.

[0059] Next, the relation between data that is additionally recorded anddesired information for example UDI will be described. On the disc, anarea in which data is additionally recorded is pre-defined with anabsolute address or the like. FIG. 11 shows an example of such an area.Data that is recorded in the area is defined as predetermined data. Data(0×22) that has been additionally recorded in the foregoing example isdifferent from known data (0×40). Thus, it can be determined that whenthe data is reproduced, it has been rewritten. The rewritten data (0×22)may be UDI data or a part thereof. In this case, since the types of datathat can be additionally recorded are restricted, it is difficult torecord many types of data.

[0060] Thus, according to the present invention, depending on whether ornot known data has been rewritten, one bit of the UDI is represented.When data has been rewritten as an example shown in FIG. 11, it isdetermined to be “1”. When data has not been rewritten, it is determinedto be “0”. When the area shown in FIGS. 11A to H are disposed N times, Nbits can be additionally recorded. In reality, N areas are furtherrepeated so as to multiply record data.

[0061] Next, the case that the present invention is applied to the CIRCwill be described. In the CIRC, four parity symbols are added. Thus, ifan error larger than five symbols takes place, it cannot be determined.Using this phenomenon, five data symbols are rewritten so that an erroris not corrected. Thus, a data sequence that has been rewritten can bereproduced.

[0062] When a decoding process is performed with the Reed-Solomon code,syndromes are calculated so as to determine whether or not there is anerror. The number of syndromes is the same as the number of paritysymbols. In the CIRC, four syndromes are calculated. When all syndromesare 0, it is determined that there is no error. Logically, when a parityof four symbols is added, if data of five data symbols is rewritten, allsyndromes become 0. However, when a syndrome value is calculated, anynumeric value cannot be substituted with any numeric value. Values withwhich any value can be substituted are restricted.

[0063] As described above, due to the restriction in the additionalrecording process for data, any data cannot be written to any data.Thus, alternatives of data sequences are decided in rewritablecombinations each of which is original data and rewritten data. Inaddition, alternatives of data sequences are decided in consideration ofadjacent data. In consideration of these two conditions, a data sequencethat can be rewritten and of which the syndrome of the rewritten datasequence becomes 0 is decided.

[0064] In the CIRC, as described above, as error correction codes, twocodes of C1 code and C2 code are used. Each data symbol is duallyencoded with these two code sequences. Thus, a data sequence that hasbeen rewritten is restored to the original data sequence by the seconderror correction code. As a result, the rewritten data cannot be read.Thus, it is necessary not to cause the two code sequences to correct anerror.

[0065] As described above, in the CIRC of which a parity of four symbolsis added, when five symbols are rewritten, all syndrome values become 0.However, when five symbols are not fixed, it is necessary to add fivesymbols that satisfy the second error correction code (C1 code). As aresult, divergence takes place. When one of five symbols is placed atany position and the other four symbols are placed in an area in which aparity is added, divergence can be prevented.

[0066]FIG. 12 to FIG. 15 describe the positions of five data symbols tobe rewritten in the CIRC. FIG. 12 shows as hatched areas the positionsof five data symbols to be rewritten out of 24 symbols of input data.These five data symbols are contained in the same C2 code sequence. Whenthe values of five data symbols are properly selected, all syndromevalues that are decoded with the C2 code become 0. FIG. 13 shows ashatched areas the positions of five data symbols on an output side ofthe C2 encoder.

[0067] An output of the C2 encoder is interleaved by an interleavecircuit and then input to the C1 encoder. FIG. 14 shows as hatched areasthe positions of five data symbols on an output side of the C1 encoder.An output of the C1 encoder is supplied to the EFM modulator through theone-symbol delay circuit. FIG. 15 shows as hatched areas the positionsof five data symbols that are input to the EFM modulator. As shown inFIG. 14 and FIG. 15, for each of five data symbols to be written, fourC1 parity symbols are rewritten so that all syndrome values become 0when they are decoded with the C1 code. Finally, 25 symbols arerewritten by the additional recording process.

[0068] Although the present invention has been shown and described withrespect to a best mode embodiment thereof, it should be understood bythose skilled in the art that the foregoing and various other changes,omissions, and additions in the form and detail thereof may be madetherein without departing from the spirit and scope of the presentinvention. For example, the present invention is not limited to anadditional recording process for a reflective film. In addition, thepresent invention can be applied to an additional recording process fora phase change film, a magneto-optical recording film, and so forth.Moreover, the present invention can be applied to an multi-sessionoptical disc on which for example CD-DA format data and CD-ROM formatdata are recorded. As information recorded on an optical disc, there arevarious types of data such as audio data, video data, still picturedata, text data, computer graphic data, game software, and computerprograms. In addition, the present invention can be applied to forexample a DVD video and a DVD-ROM.

[0069] As is clear from the foregoing description, according to thepresent invention, when an additional recording process is performed fora disc on which data has been recorded, disc identification informationor the like can be recorded in an area that has been encrypted with anerror correction code. Since the additional recording process can beperformed with an error correction code, the applicable range of theadditional recording process can be extended.

1. A data recording medium having a reflective film, a part of data in arecording area being rewritten by recording data encoded with an errorcorrection code to the reflective film so that the data is not detectedas an error when the data is decoded.
 2. The data recording medium asset forth in claim 1, wherein known data is recorded at a predeterminedposition of the recording area, part of the known data being rewritten,desired information being recorded depending on whether the part of theknown data having been rewritten.
 3. A data recording method forrecording data on a data recording medium having a reflective film, apart of data in a recording area being rewritten by recording dataencoded with an error correction code to the reflective film so that thedata is not detected as an error when the data is decoded.
 4. The datarecording method as set forth in claim 3, wherein known data is recordedat a predetermined position of the recording area, part of the knowndata being rewritten, desired information being recorded depending onwhether the part of the known data having been rewritten.
 5. A recordingapparatus for recording data on a data recording medium having areflective film, a part of data in a recording area being rewritten byrecording data encoded with an error correction code to the reflectivefilm so that the data is not detected as an error when the data isdecoded.
 6. The data recording apparatus as set forth in claim 3,wherein known data is recorded at a predetermined position of therecording area, part of the known data being rewritten, desiredinformation being recorded depending on whether the part of the knowndata having been rewritten.